FZROX vs MDY: 5% overlap
Fidelity ZERO Total Market Index and SPDR S&P MidCap 400 ETF Trust share 4.7% of their portfolios by weight — computed as Σ min(wA, wB) over every holding both funds own.
Different holding dates. These holdings were published about 3 months apart — FZROX as of 2026-04-30, the rest through 2026-07-23. Each fund is compared using its most recent file, so any trading in between shows up as a difference.
You would hold two tickers and get the diversification of 2.0. Two funds that shared nothing would score 2.0; two identical funds score 1.0.
Top shared holdings
FZROX and MDY hold 379 of the same securities. The ten contributing most to the overlap figure:
| Holding | in FZROX | in MDY | Δ |
|---|---|---|---|
| CW | 0.0% | 0.8% | 0.7% |
| XPO | 0.0% | 0.7% | 0.7% |
| UTHR | 0.0% | 0.6% | 0.6% |
| MTZ | 0.0% | 0.6% | 0.6% |
| P | 0.0% | 0.7% | 0.6% |
| TWLO | 0.0% | 0.8% | 0.7% |
| WWD | 0.0% | 0.7% | 0.7% |
| ENTG | 0.0% | 0.6% | 0.5% |
| CRS | 0.0% | 0.8% | 0.8% |
| ATI | 0.0% | 0.8% | 0.7% |
Where FZROX and MDY differ
Sector weights as a share of each fund, ordered by the size of the gap rather than the size of the sector — two funds that overlap heavily still usually diverge somewhere.
| Sector | FZROX | MDY | Δ |
|---|---|---|---|
| Information Technology | 32.3% | 13.8% | +18.4pp |
| Industrials | 9.2% | 25.4% | −16.2pp |
| Communication Services | 10.1% | 1.5% | +8.6pp |
| Real Estate | 2.3% | 6.9% | −4.6pp |
| Materials | 1.6% | 5.4% | −3.8pp |
| Unclassified | 3.8% | 0.0% | +3.8pp |
| Financials | 11.8% | 14.8% | −3.0pp |
| Consumer Staples | 4.6% | 3.1% | +1.5pp |
Δ is FZROX minus MDY, in percentage points. Sector data is not published by every issuer, so “Unclassified” is a real category rather than a gap in the table.
What each fund holds alone
95.7% of FZROX by weight, held in no part of MDY.
5.8% of MDY by weight, held in no part of FZROX.
A large count with a small weight is the usual shape: the positions one fund adds are typically its smallest ones.
Concentration and cost
| FZROX | MDY | |
|---|---|---|
| Top 10 holdings | 34.0% | 7.6% |
| Positions held | 2,685 | 400 |
| Cost per $10,000 held, per year | $0 | $23 |
Cost is the expense ratio applied to $10,000; it excludes any brokerage commission, bid-ask spread or tax consequence. Figures are facts about the funds, not a suggestion about which to hold.
Frequently asked
How much do FZROX and MDY overlap?
FZROX and MDY overlap 4.7% by portfolio weight — largely distinct portfolios. They share 379 holdings. The figure comes from current issuer holdings files (FZROX as of 2026-04-30, MDY as of 2026-07-23).
How is the overlap between FZROX and MDY calculated?
As the sum of the smaller weight in each fund, over every holding both funds own: Σ min(wA, wB). If FZROX holds a stock at 6% and MDY holds the same stock at 4%, 4% counts as shared. The result is bounded between 0% and 100%, and it is computed after looking through any fund-of-funds to the underlying holdings.
Is it redundant to hold both FZROX and MDY?
That depends on your goals — we state facts, not advice. At 4.7% overlap, each fund still contributes meaningfully distinct exposure.
What does FZROX own that MDY doesn't?
FZROX holds 2,685 positions and MDY holds 400; 2,305 of FZROX's positions don't appear in MDY at all, and they are 95.7% of FZROX by weight.
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Related comparisons
Sources: issuer holdings files, FZROX as of 2026-04-30, MDY as of 2026-07-23. Weights are fractions of each fund. Diagnostics, not advice.